ʿIsa was named head of the Office of Western Astronomy established by Kublai Khan in 1263 to study Islamic astronomical observations.[3] Kubilai would establish a Observatory for Islamic astronomy in 1271, directed by astronomer Jamal ad-Din Bukhari.[3]
ʿIsa was also instrumental in reinforcing anti-Muslim prohibitions in the Mongol realms, such as prohibiting halal slaughter and circumcision, and, according to Rashid-al-Din Hamadani encouraged denunciation of Muslims.[4] ʿIsa also showed to Khubilai the Sword Verse of the Quran, raising the suspicion of the Mongols towards Muslims.[4] According to Rashid al-Din, as a result, "most Muslims left Khitai [China]".[4]
Diplomat to Europe
Isa Kelemechi was later a member of the first mission to Europe sent by Arghun, the Il-Khan in 1285. He met with Pope Honorius IV, remitting a letter from Ghazan offering to "remove" the Saracenz and divide "the land of Sham, namely Egypt" with the Franks.[5][6] The message, written in imperfect Latin, said:
"And now let it be [says the Il-Khan], because the land of the Saracens is not ours, between us, good father, us who are on this side and you who are on your side; the land of Scami [Sham] to wit the land of Egypt between you and us we will crush. We send you the said messengers and [ask] you to send an expedition and army to the land of Egypt, and it shall be now that we from this side shall crush it between us with good men; and that you send us by a good man where you wish the aforesaid done. The Saracens from the midst of us we shall lift and the Lord Pope and the Cam [Great Khan Qubilai] will be lords".